Milk proteins can be divided into two general classes, namely, the serum or whey proteins and the curd or casein products. Casein is generally classified as a phosphoprotein but in reality is a heterogeneous complex of several distinct and identifiable proteins (alpha, beta, kappa, et cetera, proteins), phospherous and calcium which complex takes the form of a colloidal calcium salt aggregate in milk called calcium caseinate. During the production of cheese, casein is precipitated from the milk by one of two methods. The first involves the treatment of the milk with acid to lower the pH to about 4.7 whereupon the casein proteins precipitate from the milk to form the curd which will ultimately be processed to cheese. In the alternative process, the precipitation of the casein is accomplished using a rennet enzyme rather than acid. The casein produced by the former process is generally higher in fat and lower in ash than the corresponding product derived from the latter process. The difference in the ash content is believed to be a result of calcium phosphate being split off of the casein molecules by the action of the acid, with the residual ash being mostly organically bound phospherous. The "acid casein" is used in the production of soft cheeses such as cottage cheese, while the "rennet casein" or "para-casein" is utilized in the manufacture of cheeses such as cheddar or mozzarella.
Whey is the serum remaining after the solids (fat and casein) are removed from the milk. Whey comprises lactalbumin and lactoglobulin proteins. Lactalbumin makes up 2% to 5% of the total skim milk protein and is believed to function in milk as a proteinaceous surfactant stabilizer of the fat particles. Lactoglobulin makes up another 7% to 12% of the total skim milk protein and is closely associated with the casein protein in whole milk. Whey derived from the acid precipitation process mentioned above is referred to as acid or sour whey and generally has a pH of about 4.3 to 4.6. Whey derived from the enzymatic precipitation process, also mentioned above, is referred to as sweet whey and generally has a pH of from about 5.9 to about 6.5. As a generalization, commercial dried whey comprises about 10% to 13% denatured protein, 71% lactose, about 2% lactic acid, about 3% to 5% water, about 8% to 11% ash, and includes a low concentration of phosphoric anhydride. As derived from the cheese making process, whey generally is an aqueous medium comprising 90% or more water. The respective characteristics of sweet and acid wheys are summarized below:
______________________________________ Sweet Acid ______________________________________ Lactose 4.0 to 5.0% 4.0 to 5.0% Dry Solids 5.3 to 6.6% 5.3 to 6.0% Proteins 0.6 to 0.8% 0.6 to 0.7% Minerals & Salts* 0.4 to 0.6% 0.7 to 0.8% Fats 0.2 to 0.4% 0.05 to 0.1% ______________________________________ *Primarily Na.sup.+, K.sup.+ and Ca.sup.++ salts It is noted that U.S. Pat. No. 4,358,464 discloses a proposal for converting acid whey to sweet whey.
The volume of whey produced is directly proportional to the volume of cheese production. One estimate for the United States alone, placed whey production on the order of 43.6 billion pounds per year.
Although both whey itself and whey components such as the whey proteins lactalbumin and lactoglobulin and the sugar lactose all have various known utilities, there are significant difficulties in converting the whey into industrially useful forms. The fundamental difficulty is that whey as obtained from the cheese making process contains, as mentioned above, about 90% water and none of the components are generally useful in that form. The removal of the excess water is very expensive and is most likely to remain so in view of present and projected energy costs. Moreover, the useful proteins contained in whey make up only a minor proportion, some 9% to 11% by weight, of the whey solids. The major portion of the balance of the whey solids, ie. greater than 70% by weight thereof, is lactose. The commercial value of lactose was and is, however, quite low. The end result was that whey was generally considered by the cheese maker to have little value and indeed, as merely an item to be disposed of at the least possible cost. Quite often the whey was merely dumped, by draining to sewer. In more recent times, however, increased awareness of the possible pollution of the environment has resulted in the imposition of severe restrictions on such disposal methods to the extent where whey became almost a liability in the context of the cheese making process. Although some local authorities will accept whey and its related products for treatment in their sewage systems, their charge for doing so is very high. One of the alternatives which then became feasible in order to reduce the costs associated with whey disposal, was to heat the by-product so as to heat denature and coaggulate the protein, principally lactalbumin, which could then be separated in a coarse, non-functional form from the residual lactose syrup. The resulting products were then sold to defer the processing costs to below the disposal costs. More preferably the whey was then simply dried using spray, drum or freeze drying and the like, to produce a hygroscopic product. Typical of the products produced by such means are dried whey animal feed supplements comprising a minimum of 65% lactose and about 12% protein. These supplements have higher concentrations of riboflavin than does skim milk and the supplements are generally valued in feed mixtures as a source of this and other solubles (see Encyclopedia of Chemical Technology, Vol. 6, page 308).
If these latter processes are controlled, recrystallization of the lactose can be effected and a more useful non-hygroscopic product is obtainable. Crystaline precipitation of lactose can also be utilized to slightly enhance the protein content of these products. Such procedures further offset the processing costs by producing a slightly more valuable product. However, the dried products retain, to a significant extent, the characteristic whey odour and especially taste, which limit their commercial utility. Such products generally have very little value-added relative to whey and are used mostly as additives in the baking industry because of the water absorption capacity of the denatured proteins.
As a consequence of the severe disposal problems besetting the industry and the possibility of realizing a significant economic return over and above processing costs through the sale of concentrated or upgraded whey protein and other whey censtituents, there has been much expenditure of time and money in whey treatment research and development in recent years. Most of these efforts have dealt with isolating or concentrating the protein. One process for recovering whey proteins is known in the art as the "centri-whey" process and comprises denaturing the native whey proteins by heat treatment at a pH of from 4.5 to 4.6 and subsequently isolating the denatured proteins by centrifugation. Only about 70% of the whey proteins are denatured using this process and the balance is lost to the supernatent following contrifugation. This inefficiency notwithstanding and assuming the functional attributes of native whey proteins are not required in a given application, denatured whey proteins are preferred, in part because they are, according to U.K. specification No. 2,020,667, more readily digested than are the native undenatured proteins. Denaturation, in the context of protein chemistry, covers a range of changes in the molecular structuring of proteins that may be induced, for example, by heating a protein solution beyond the point which is characteristic for each protein and/or by exposing it to acids, alkalies or various detergents. An irreversibly denatured protein has a reduced solubility relative to its undenatured or native state as well it cannot be crystalized. The denaturation process involves the rupture of inter-molecular hydrogen bonds such that the highly ordered structure of the native protein is replaced by a more random structure. While denaturation is usually irreversible, there are some instances, depending on the protein being treated and the treatment to which the protein is subjected, which are reversible. Some of the differences between the properties of native and denatured whey proteins have been reported in the relevant literature. Reference will be made herein to such differences between the native and denatured whey proteins as bear on their respective utilities. At some point towards the end of the denaturation process, changes occur which are directly perceivable by unaided human senses which generally involve gelling, thickening and the development of opacity. This stage of the process is hereinafter refered to as coagulation.
Other processes for concentrating whey proteins utilize ultra-filtration techniques. For example, one known method in volves subjecting whole whey to an ultra-filtration step whereby a lactose syrup and a soluble, undenatured whey protein concentrate (WPC) is obtained. The WPC is disclosed as being both soluble at low pH and therefore useful in high nutrition beverages, and coagulable by heat to produce an egg white replacer. To the best of the present inventors' knowledge, the WPC resulting from this process has never been used commercially in the latter capacity, presumably because current economics appear to favour natural egg whites in most applications. In any case, the solubility and coagulability of this WPC are derived from the functional characteristics retained by the undenatured whey proteins. It is noted once again, however, that in applications, where those functionally derived characteristics are not specifically required, denatured whey proteins are reported to be more easily digested and, moreover, impart characteristics such as water adsorption or colour and heat stability attributes desirable in certain applications, which attributes are not available from undenatured whey proteins.
As another example of ultrafiltration is whey processing, U.K. specification No. 2,020,667 teaches a process wherein whey proteins are recovered from whole whey by subjecting the whole whey to a heat treatment to denature and insolubilize the proteins which are then recovered from the liquid medium by ultra-filtration. This process is disclosed as being more cost-effective and more yield-efficient than the above-mentioned "centri-whey" process in that the undenatured whey proteins (30%) are retained together with the denatured proteins in the ultra-filtered retentate rather than being lost to the centrifuged supernatent.
U.S. Pat. No. 3,896,241 describes another process for producing a soluble whey protein concentrate having a low microbial count in which whey from bovine milk is passed through a diatomaceous earth filter to remove residual casein and milk fat; and subsequently subjected to an ultra-filtration step which removes the major part of the water, lactose and mineral salts leaving a whey protein concentrate. This concentrate is then passed through a strongly acidic cationic exchange resin to further reduce the mineral salt level in the product and reduce the pH, the latter being reduced further if desired by the addition of acid. This concentrate is then dried in the normal manner such as by spray drying.
U.S. Pat. No. 4,235,937 discloses a process for treating a variety of protein sources by utilizing a technique other than ultra-filtration with particular emphasis being placed on the treatment of whey. An important feature of that treatment is that the whey, which is whole whey having the usual low total solids and high lactose content, must be fresh or nearly fresh. Moreover, from the time of its production in the cheesemaking process to its being processed according to the disclosed process, its temperature must not be allowed to drop to any significant extent. In fact, the minimum temperature at which the whey must be maintained prior to processing is disclosed as being 90 degrees Fairenheit. The process involves subjecting the whey to "blending shear forces" in the presence of a metal gluconate solution which functions as a blandness imparting agent and a colloid enhancer component, the reaction mixture during the blending being maintained at an elevated temperature but one which is below the denaturing temperatures of the proteins present. The above agents are also said to assist in effecting the important automatic decanting feature of the process. The process disclosed in this patent is intended to avoid denaturation of the whey protein and any protein that is denatured and contained in the automatically decanting floc is by definition of a large particle size.
U.S. Pat. No. 3,852,506 discloses a process for making dry, agglomerated, soluble whey protein which is relatively bland and readily reconstituted into a liquid form, the process comprising mechanically dividing spray dried, demineralized, spheres of whey protein isolate to a particle size less than forty-four (44) microns, which particles are then agglomerated obviously to larger sized particles. It should be noted that spray-drying of whey, in common with the other usual methods of drying whey usually produces a dried product having a particle size of from about 75 microns to 200 microns and usually toward the upper end of that range. The inventors, although unaware of the precise mechanism by which the process achieves the desired objectives, believe that it is the specific mechanical manner of forming the subdivided particles, namely grinding, which provides the desired result, namely a relatively bland product. The particle size characteristic is apparently required to assist in dispersing the dried product in liquid to accelerate solubilization therein. U.S. Pat. No. 4,225,629 describes another process for the production of an insoluble protein concentrate which, in this case, also contains carbohydrates such as starch, vitamins and a relatively high percentage of fat. In this process a mixture of whey and a protein--containing seed product is adjusted to a pH of about 9-10; the resulting juice, which contains soluble proteins, is separated therefrom and acidified to an acid pH, following which the protein is precipitated by heat or by the addition of sodium hexametaphosphate, and the precipitate separated, washed with water and dried by known methods such as drum-drying or freeze-drying. In contrast to preparing simple protein concentrates, U.S. Pat. No. 4,218,490 discloses a process for preparing an edible foodstuff incorporating a proteinaceous surface-active agent. The surface-active agent contains more than ninety (90) percent of protein and is a functional protein obtainable from a large variety of protein sources including soya, blood, whey and oil seeds by ion-exchange extraction followed by drying. The use of soluble whey lactalbumins in this application appears to be similar to the role these same proteins play in the stabilization of fat particles in milk. As is usual with such agents, it is used in relatively small amounts based on the amount of food involved. Indeed, this agent is generally used as a minor component of the total amount of such functional agents used in any particular application.
All of the foregoing processes which result in insoluble denatured protein products involve, for the most part, heat denaturing the whey at about, or above, the whey's isoelectric point. According to Modler et al, Journal of Dairy Science, Volume 60, No. 2, such processes are both popular and economical in the recovery of whey proteins but the resulting products are generally insoluble and gritty, and the scope of their commercial application is limited accordingly. Improvements in solubility have been reported by Amantea et al in the Journal of Canadian Institute of Food Science and Technology 7:199, 1974 in whey proteins which were iron-fortified then treated under alkaline conditions: but these improvements are realized only through extensive depletion of sulphur-containing amino acids. Processes carried out below the isoelectric point of the whey protein in question are reported by Modler at el to generally result in improved solubility and functionality. A similar process is described in U.S. Pat. No. 3,930,039 wherein it is expressly disclosed that only a very small fraction of the total whey protein is denatured under highly acid/elevated temperature conditions which leaves the balance of the protein in its native functional and hence, soluble condition.
Obviously, soluble native whey protein does not contribute a gritty texture to foods fortified with same nor does it contribute an emulsion-like texture. Moreover, difficulties have been encountered in utilizing such soluble whey protein in fortification of pasta, as is disclosed in Food Processing, 36, (10) 52, 54 (1975). According to this article, USDA scientists at the Eastern Regional Research Centre in Philadelphia found that conventional native (soluble) whey protein products were unacceptable for use in fortification of pastas without extensive and radical alterations to the processing equipment used in the manufacture of unfortified pastas. Heat denatured whey protein products do not require such modifications to the existing pasta-making equipment. Product evaluation of such denatured whey protein fortified pasta by a trained taste panel established that the denatured whey protein fortified pasta had an inferior texture to unfortified pasta. This finding is not surprising in view of the expected gritty character of heat denatured whey proteins. While the taste panel found that the difference in texture would not render the fortified products commercially unacceptable, particularly as tomato and cheese sauces further mask the differences, it is clear on the face of it that the fortified product would be more commercially acceptable if the texture could be inherently improved upon rather than simply masked. However, as pointed out by Modler et al, supra, the large particle size of the protein agglomerates formed by the above-mentioned whey protein denaturing processes result in products having a gritty mouth feel. This operates to restrict the product's commercial utility even as a protein supplement.
Similar organoleptic problems have been encountered in the use of soya bean derived protein in calorie reduced foods, as is disclosed in U.S. Pat. No. 4,041,187. That patent points out that the use of mechanical size-reducing apparatus has been generally unsuccessful in obtaining the desired results. A similar situation has been encountered in respect of whey protein as is reflected in an article appearing in the New Zealand Journal of Dairy Science and Technology, 15, 167-176, by J. L. Short. The data disclosed in Table 2 of that article demonstrates that most of the traditional techniques utilized in the manufacture of the heat-precipitated (denatured) whey protein isolate results in protein particle sizes ranging from about 100 to about 200 microns, even after grinding or other mechanical particle size reducing treatments. Even the relatively smaller denatured whey protein particles (about 28 microns) disclosed by Short contribute a coarse, gritty texture to foods so supplemented.
It is noteable that undenatured "spherical" whey protein particles having a mean particle size of about 28 microns can be obtained by spray drying the whey protein concentrate. Even though such particle sizes are of the same order of magnitude as fat particles in milk (1 micron to 22 microns, with a 5 millimicron membrane believed to comprise a protein phospholipid and high melting point triglyceride complex) the rheological properties of the respective whey and fat particles is significantly different with the result that when fully hydrated and dispersed the proteins, being mostly undenatured, resolubilize and lose their particulate identity, creating somewhat viscous, sticky solutions typical of soluble proteins which, of course, cannot approximate the mount feel associated with the fat particles.
In addition to the clear advantages of utilizing low calorie substitutes for fats and oils in calorie reduced foods, there are shelf-life considerations which could make stable fat substitutes highly desirable. This is particularly true in foods such as salad dressings and mayonnaise products. As stated in the Encyclopedia of Chemical Technology, Volume 12, page 38,
"in no other fatty food product is oil subjected to so many unfavourable conditions which tend to turn it rancid or to cause it to deteriorate in other ways. Time, temperature, light, air, exposed surface, moisture, nitrogenous organic material, and traces of metals are known to be factors responsible for rancidity. In salad dressings and mayonnaise products, the oil is subjected similtaneously to most or all of these adverse conditions."
To be widely acceptable, any replacement for such fats and oils in emulsified food products should closely approximate the organoleptic characteristics of the oil or fat to be replaced. Principal amongst those characteristics are the attributes of mouth feel and clearly a gritty product will be entirely unacceptable in such an application.
In contradistinction to the previously mentioned documents which are concerned with the protein component of whey, U.S. Pat. No. 4,143,174 and its divisional application Ser. No. 965,270, now U.S. Pat. No. 4,209,503, teach using vegetable as well as dairy wheys as sources of a non-protein colloidal precipitate which is useful as a functional food modifier capable of modifying food compositions into which they are incorporated, and in particular, the stabilization, emulsification, thickening, clouding, gelling and viscous properties of such compositions. The precipitate is non-proteinaceous in nature, although a small proportion of protein, up to five percent (5%) of the complex, may be present, this essentially being considered as a contaminant which is non-deleterious to the present precipitate, apart from having a nominal dilution effect. The precipitate has a particle size of less than 10 microns and more particularly, in the range of about 1 millimicron to about 1 micron. Preferably, it is obtained from the non-protein ultra-filtration fraction of whey and the whey, or the non-protein fraction thereof, is concentrated up to about 30% solids. The precipitate may be obtained by raising the pH of the whey or fraction thereof to between a pH of between 5 and 9, usually between about 5.8 and 7.2, and then heating until the desired precipitate is formed. It may be dried by any conventional means but generally at temperatures at less than one hundred and eighty (180) degrees Fahrenheit, since above that temperature "browning" may occur. The precipitate will comprise from as little as 0.01 percent to as much as 30% but generally from 0.5 percent to about 20-25% of the food composition in which it is incorporated. Being non-proteinaceous in nature, however, these precipitates are not useful in increasing the foods' PER (Protein Efficiency Ratio) value. Generally, protein fortification of foods has been carried out using fish, soy, whey, casein, egg albumin or gluten protein sources. Each of these fortifying agents has its attendant problems. Soy protein, for example, develops a typical off-flavour over time, even if it is very carefully prepared. Fish proteins all have objectional off-flavours. Egg albumins, in order to be stabilized in a commercially-practical dry form, require enzymatic treatments which unfortunately also produce a fishy off-flavour. Gluten proteins can be used but these have a low PER. Whey has already been mentioned hereinbefore and the problems attendant its use are clearly set out above. As a consequence of the problems associated with protein fortification using such agents other than whey, the use of such other agents has been restricted to very low levels or to use in products wherein their objectionable character can be masked. They are not considered to be useful in bland, or subtly flavoured, food products.
In summary, soluble food protein is generally gluey, while thermally denatured proteins tend either to manifest as massive gels (such as cooked egg whites, for example) or as coarse, gritty particles. One notable exception to this generalization arises in the case of soy proteins which have been successfully spun into fibres having organoleptic properties (texture, specifically) that are reminiscent of myofibrilar substances, such as meats. That texture is obviously not universally applicable, however, since such fibres clearly do not emmulate in any respect the mouth feel one might expect to experience, for example, with fats or oils.
It remains only to be noted that, according to The Whey Products Institute as quoted in The FDA Consumer--November 1983, only 53% of the 43.6 billion pounds of whey produced annually in the United States is currently being processed into useful whey products.
It is an object of the present invention to provide a new and useful form of whey proteins and a process for the production thereof.